1. Field of the Invention
The present invention relates to a radio apparatus and radio receiving method capable of performing radio transmission and reception at the same time.
2. Description of the Related Art
Multimode radio apparatuses have been made available in recent years that are radios or radio devices that can be used in multiple modes such as multiple frequency bands.
For example, Japanese Patent Application Laid-Open Publication No. 2000-13274 discloses a multimode radio apparatus including CDMA (Code Division Multiplex Access) and PDC (Personal Digital Cellular System) transmission units. The technique in Japanese Patent Application Laid-Open Publication No. 2000-13274 can reduce the number of components in transmission units by sharing circuits between the wideband CDMA and PDC transmission units.
Japanese Patent Application Laid-Open Publication No. 2003-133981 discloses a reception unit of a multimode radio apparatus that receives wideband and narrowband signals. The technique in Japanese Patent Application Laid-Open Publication No. 2003-133981 can reduce the size of the apparatus by sharing circuits of the reception unit between the two modes.
When transmission and reception of signals are performed based on more than one standard in an apparatus, that is, transmission is performed based on one standard and reception is performed based on another standard, a signal transmitted by the apparatus cross-talks into a signal received by the apparatus.
In that case, the reception signal intensity becomes very strong because the transmitting and receiving circuits are close to each other. Consequently, the transmission signal acts as an interference wave or noise that interferes with the target reception signal that the receiver is expected to receive.
Japanese Patent Application Laid-Open Publication No. 2007-505591 discloses that a vector multiplier is used in a multimode radio transmission and reception unit to reduce or eliminate interference with a receiver caused by a transmitter while the transmitter is transmitting a transmission signal to an antenna and at the same time a receiver is receiving a signal in another mode from the antenna.
The vector multiplier controls the phase and amplitude of noise that cross-talks into the receiver (that is, spurious noise).
The configuration for adjusting the phase and amplitude as described in Japanese Patent Application Laid-Open Publication No. 2007-505591 has the drawback that the configuration increases the complexity and size of the circuitry as well as the cost.